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Video Trickery

Short answer: Many CMOS image sensors use a rolling shutter: instead of capturing every pixel at the same instant, they read the frame out row by row, usually top to bottom. When something moves fast during that readout, or the camera itself moves, each row records it at a slightly different moment.

The result is skew, wobble ('jello') or strange shapes, like propeller blades that look curved or detached, and flashes that light only part of a frame. A global shutter exposes all pixels at once and avoids this. The footage shows spinning blades and strings distorted on camera.

VideoWrite-up1 sources

In collections:Everyday Physics

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What should you know about Video Trickery?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Rolling shutters read the frame row by row.

    DD-301-F01 · Write-up · Exhibit A (Row by row)

  2. Global shutters expose all pixels at once.

    DD-301-F02 · Write-up · Exhibit E (Global shutter)

Video transcript: Video Trickery: Phone Videos Can Bend Propellers

DID YOU KNOW? The rolling shutter effect is a distortion phenomenon that occurs when capturing fast moving objects or when the camera itself moves quickly. This effect is common in cameras with CMOS sensors which capture images by scanning across the scene from top to bottom or vice versa, rather than capturing the entire image at once. As a result objects moving quickly across the frame can appear skewed, leaning, or warped as different parts of the object are captured at slightly different times. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 24.5s Reel ·

Video coming soonVideo Trickery · Instagram Reel
Video Trickery: Phone Videos Can Bend Propellers Instagram Reel · · 24.5s

The write-up

Phone videos can bend propellers. A rolling shutter reads the sensor line by line, not all at once.

  1. Exhibit A

    Row by row

    A rolling shutter reads the frame row by row instead of all at once.

  2. Exhibit B

    CMOS sensors

    Many CMOS sensors use a rolling shutter.

  3. Exhibit C

    Skew and wobble

    Fast motion during readout causes skew and wobble.

  4. Exhibit D

    Odd propellers

    Spinning blades can look curved or detached.

  5. Exhibit E

    Global shutter

    A global shutter exposes all pixels at once and avoids the effect.

Questions people ask about Video Trickery

How does a rolling shutter read a frame?

Usually top to bottom.

Source: Write-up · Exhibit A (Row by row) · Wikipedia: Rolling shutter

Which sensors commonly use rolling shutters?

Many phone cameras do.

Source: Write-up · Exhibit B (CMOS sensors) · Wikipedia: Rolling shutter

What causes the distortion?

Each row sees a different moment.

Source: Write-up · Exhibit C (Skew and wobble) · Wikipedia: Rolling shutter

How can propellers look on video?

The blades move between rows.

Source: Write-up · Exhibit D (Odd propellers) · Wikipedia: Rolling shutter

What avoids the effect?

It exposes every pixel at once.

Source: Write-up · Exhibit E (Global shutter) · Wikipedia: Rolling shutter

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. How does a rolling shutter read a frame?

    1. Row by row
    2. All at once
    3. Randomly
    4. By color
    Show the answer

    Answer: A. Row by row Usually top to bottom. Source: Write-up · Exhibit A (Row by row) · Wikipedia: Rolling shutter

  2. Which sensors commonly use rolling shutters?

    1. CMOS
    2. Film
    3. Vacuum tubes
    4. Mirrors
    Show the answer

    Answer: A. CMOS Many phone cameras do. Source: Write-up · Exhibit B (CMOS sensors) · Wikipedia: Rolling shutter

  3. What causes the distortion?

    1. Motion during readout
    2. Low battery
    3. Dust
    4. Heat
    Show the answer

    Answer: A. Motion during readout Each row sees a different moment. Source: Write-up · Exhibit C (Skew and wobble) · Wikipedia: Rolling shutter

  4. How can propellers look on video?

    1. Curved or detached
    2. Invisible always
    3. Square
    4. Doubled in size
    Show the answer

    Answer: A. Curved or detached The blades move between rows. Source: Write-up · Exhibit D (Odd propellers) · Wikipedia: Rolling shutter

  5. What avoids the effect?

    1. A global shutter
    2. A bigger lens
    3. More zoom
    4. A tripod only
    Show the answer

    Answer: A. A global shutter It exposes every pixel at once. Source: Write-up · Exhibit E (Global shutter) · Wikipedia: Rolling shutter

Cite this case file

Easterling, Marcus. "Video Trickery." The Detail Department (DetailEnjoyer), case file DD-301, last updated Aug 16, 2024. https://detailenjoyer.com/case/video-trickery/

Permalink: https://detailenjoyer.com/case/video-trickery/ · Last updated

Markdown version

Cite a single fact by its ID, for example DD-301-F01 → https://detailenjoyer.com/case/video-trickery/#DD-301-F01

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